The initial steps of vision, the transduction and encoding of physical light stimuli into neural signals, occur in the retina, an out-pocketing of the diencephalon of the brain that lines the back of the eye. Retinal circuits are reconfigured according to the prevailing illumination conditions through the action of modulatory retinal neurotransmitters such as dopamine. The long-term goal of the line of research proposed here, is to elucidate the underlying cellular and molecular mechanisms by which retinal function is reconfigured by neuromodulatory signals. For the upcoming award period, we propose to focus on two critical questions in retinal neurobiology related to feedback circuits in the retina - How retinal dopaminergic neurons, the source of retinal dopamine, are regulated by light, and whether connexin hemichannels may contribute to feedback at the first visual synapse. We propose the following 2 specific aims: Aim I. Using a transgenic mouse model developed in our laboratory that enables in situ recording from dopaminergic amacrine neurons (DA neurons), we will further define the synaptic mechanisms regulating sustained, transient and resting DA neuron activity and dopamine neuron heterogeneity. Aim II: Using the zebrafish molecular genetic model system we will combine electrophysiological analysis of native horizontal cell hemichannel currents and horizontal cell feedback to cones with connexin gene manipulation to decisively test the participation of hemichannels in feedback. Completion of these aims will provide information fundamental for understanding normal retinal function and contribute to our understanding of clinically relevant dopaminergic mechanisms associated with photoreceptor degeneration, myopia, and visual deficits in Parkinsonism and diabetic retinopathy.